We will investigate the in vitro and in vivo biotransformation of hexachlorobenzene (HCB), particularly the formation of dechlorination products, phenols and reactive metabolites, and establish whether covalent binding of the latter compounds to cellular proteins occurs. The modified proteins will be isolated and characterized, the sites of covalent attachment identified, and the nature of the bound metabolites determined. The synthesis and destruction of porphyrins in the experimental animal and in liver cells in vitro and the effects of administration of HCB and its metabolites on a number of biochemical parameters will also be investigated in an attempt to correlate the nature of the metabolite and covalent binding with the expression of toxicity and the development of porphyria.